Electrostatic sheet hold-down



March 1965 w. c. ROBERTS ETAL 3,174,748

ELECTROSTATIC SHEET HOLD-DOWN Filed June 17, 1963 2 Sheets-Sheet 1 INVENTQRS WEBSTER C. ROBERTS BY G. HERMAN BRANDT ATTO NEYS March 23, 1965 w. c. ROBERTS ETAL 3,174,748

' ELECTROSTATIC SHEET HOLD-DOWN Filed June 17. 1963 2 Sheets-Sheet 2 FIG.- 6

INVENTORS WEBSTER C. ROBERTS BY G. H ERMAN BRANDT ATTORNEYS United States Patent 3,174,748 ELECTROSTATIC SHEET HOLD-DOWN Webster C. Roberts, South Euclid, and Gotlieb Herman Brandt, Shaker Heights, Ohio, assignors to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Filed June 17, 1963, Ser. No. 288,251 18 Claims. (Cl. 271-8) The present invention relates to devices for establishing electrostatic fields and, more particularly, to such a device for use in holding a sheet against a member with which the sheet is movable.

Electrostatic devices have been used in sheet-handling machines, such as printing presses, to cause sheet material to hug a member with which the sheet is movable. However, problems have been encountered in causing the sheet to hug the member without producing wrinkling of the sheet, particularly when the sheet is carried between members which cooperate to form a nip. Various attempts have been made to prevent the wrinkling of the sheet as it is carried through a nip and as disclosed in the copending application of Gotlieb Herman Brandt, Serial No. 244,403, filed December 13, 1962, assigned to the present assignee, one such method is to provide an electrostatic field transversely of the sheet which has different magnitudes progressing across the sheet and increasing with the strength of the field from each side edge of the sheet to the central portion thereof. The aforesaid patent application discloses a device for establishing a nonuniform field.

One problem of the device disclosed in the foregoing application is that it presents somewhat of a hazard to operating personnel of the press, since the device for establishing the field comprises an elongated conductor extending parallel to the sheet but displaced therefrom and a plurality of ionizing needles extending from the conductor toward the sheet. When attempts were made to provide insulation about the electrostatic field device, it was found that the field between the needles and the sheet was adversely affected and in the case of nonuniform fields, the nonuniformity of the field was destroyed. Accordingly, an important object of the present invention is the provision of a new and an improved electrostatic device for controlling the effect of an insulator disposed about an ionizing conductor on the field produced by the ionizing conductor and preferably for establishing a nonuniform field along the length of the device and between the device and a cooperating member with the device being so constructed and arranged that it does not constitute a hazard to operating personnel.

A further object of the present invention is to provide a new and improved device for use in establishing a non uniform electrostatic field in which the intensities of various portions of the field may be readily controlled.

In accordance with the preferred embodiment of the present invention, an elongated conductive member to which one side of a high voltage supply is connected for establishing an electrostatic field is protected with a covering of insulating material, the insulating material having opening means therein for exposing the conductive member to establish the electrostatic field. The insulating material for the elongated member has conductive material thereon or immediately adjacent thereto which is insulated from the elongated member. Preferably the conductor member is connected to the other side of the power supply to control the electrostatic field established by the elongated member. In the preferred and illustrated embodiment, the elongated conductive member comprises a rod from which spaced ionizing needles extend radially in one direction. The insulating material is in the form 3,174,748 Patented Mar. 23, 1965 of a tube which encompasses the metal rod and the needles and which has openings opposite the ends of the needles to expose the needles. The outer side of the tube is provided with conductive means which, in the preferred and illustrated embodiment, is grounded, i.e., connected to the opposite side of the high voltage supply to which the electrostatic device is connected, to control the field strength at various places along the length of the conductive members. The conductive material may be movable to adjust the field distribution.

Further objects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment thereof made with reference to the accompanying drawings forming a part of the present specification for all matters disclosed therein and in which:

FIG. 1 is a fragmentary sectional view of a printing press embodying the present invention;

FIG. 2 is a view looking approximately from along line 2-2 of FIG. 1;

FIG. 3 is a view taken approximately along line 33 of FIG. 1;

FIG. 4 is a fragmentary view looking approximately from line 4-4 of FIG. 3;

FIG. 5 is a fragmentary perspective view of a modified form of the present invention; and

FIG. 6 is an elevational view of another modified form of the present invention.

While the present invention is useful in various machines wherein it is desirable to cause a sheet to hug a by high voltage energy, it is particularly useful in a printing press to prevent a sheet being carried by an impression cylinder through a nip formed by the impression cylinder and a printing cylinder from slapping against the printing cylinder. Accordingly, the invention is shown as embodied in such a printing press.

Referring to the drawings, FIG. 1 illustrates a portion of a printing press having a plate cylinder 10, a blanket or printing cylinder 11 cooperating with the plate cylinder 10 and an impression cylinder 12 which cooperates with the blanket cylinder 11. The plate cylinder 10 is disposed above the blanket cylinder and carries the printing plate which has the image to be printed formed thereon and is inked by conventional means, not shown in the drawings, to effect a transfer of the image on the plate to the blanket cylinder 11. The image on the blanket cylinder 11 is printed onto a sheet of material carried by the impression cylinder 12 disposed below and to one side of the blanket cylinder, the sheet passing between the impression cylinder 12 and the blanket cylinder 11 as the cylinders are rotated. The cylinders 11 and 12 form a nip into which the sheet is carried and the sheet is printed as it is drawn between the cylinders 11 and 12. The cylinders 10, 11, 12 are rotatably supported on respective shafts which extend between and are journaled in spaced side frames of the press. The sheet which is to be printed is indicated by the reference numeral 14 and is fed to the impression cylinder 12 by means shown as a conventional transfer cylinder 12a which may constitute part of any conventional feeding means not shown or described in the present application, or in the case of a multiun-it press, the cylinder 12a may be the trans: fer cylinder between units. Suffice it to say that the impression cylinder 12 is provided with gripper fingers 15 that grip the leading edge of the sheet as it is fed to the impression cylinder so that the sheet will rotate therewith. The sheet 14 is transferred to the impression cylinder at a point in advance of the nip formed by the blanket cylinder 11 and the impression cylinder 12 and the fingers 15 are operated by conventional cam means to release the sheet thereon for delivery to a delivery :3 cylinder which cooperates with the impression cylinder or to another transfer cylinder 16a for transferring the sheet from the printing unit shown to a succeeding printing unit. The cylinders 10, 11, 12 and 12a are intergeared and are rotated by conventional drive means in a manner well understood by those skilled in the art and not necessary-for an understanding of the present invention. The printing press thus far described is of conventional construction and the above description will be sufficient for those skilled in the art to understand the environment of the present invention and the manner in which it functions.

When a sheet is fed to the impression cylinder 12 and and the fingers 15 operated to secure the sheet thereto, some air is inevitably trapped under the sheet 14. As the impression cylinder 12 is rotated to advance the sheet 14 so that its leading edge thereof enters the nip of the cylinders 11, 12, the air beneath the sheet 14 is pressed out as the sheet passes between the cylinders and builds up under the sheet and tends to form a bubble there immediately adjacent the nip. As the rotation of the impression cylinder 12 continues, air actually causes the sheet 14 to, what may be termed, float relative to the impression cylinder 12 and as the trailing edge of the sheet approaches the nip, the air thereunder tends to explode and to cause, together with centrifugal force, the trailing edge to flap against the blanket cylinder 11. It has been found, as described in Patent No. 3,039,388, issued June 19, 1962, that this flapping may be prevented by electrically attracting the sheet to the cylinder 12. In the illustrated embodiment, the sheet is electrically attracted to the cylinder 12 by subjecting the sheet to spaced electrostatic fields formed ahead of the nipby electrostatic devices20, '20 which lie adjacent to the outer periphery of the cylinder 12 in planes containing the axes of the cylinder. The field of these devices ionizes the air and causes a sheet passing through the field to hug the cylinder 12.

The electrostatic device 2t) is adjacent to the nip and the device is spaced rearwardly therefrom along the circumference of cylinder 12. The device 20 is shown in detail in FIG. 3 and, as shown therein, comprises a tube'21 of nonconductive material, having open ends closed by plugs 22, 23 of insulating material. The plugs 22, 23 support an internal bar 24 disposed coaxially with the tube and formed of electrically conductive material, such as aluminum. The bar is smaller in diameter than the inside diameter of the tube so as to provide space about the bar and the bar has a plurality of pins or needles 25 having pointed end portions extending radially therefrom toward the impression cylinder 12. In the illustrated embodiment, the needles25 are uniformly spaced and the tube 21 has an opening or an aperture 26 adjacent the outer end of each of the needles.

.A high voltage generator 27, having one side thereof grounded, and a high voltage terminal'28 are provided. The high voltage terminal 28 is connected to the bar 24 through a valve device V to establish an electrostatic field between the needles 25 and the impression cylinder 12, which is a grounded metal cylinder. The valve V may be adjusted to vary the strength of the field. The connection to the bar 24 from the valve V is made through a radially extending opening 29 in a portion of the plug 22 extending outwardly of the end of the tube 21. The bar 24 is drilled at 30 adjacent the opening 29 to receive the connection from the valve V and a setscrew 31 is threaded into the end of the bar 24 to engage the connection and clamp it in the drilled opening 30. Access to the screw 31 is provided by an axial opening 32 in the end of the plug 22.

The device 20' may be a duplicate of the device 29 with the device being connected to the high voltage generator 27 through a valve corresponding to the valve V.

Also, a corresponding electrostatic device 26" may be provided adjacent the circumference of the cylinder 12 at the exit side of the nip. Such device 26 would be particularly useful in a lithographic printing press where 4 the sheet tends to hug the blanket cylinder. The device 20 will maintain an attraction between a sheet and the cylinder 12 and help to strip the sheet material from the blanket cylinder.

In accordance with one aspect of the present invention, a grounded conductor, i.e., a conductor connected to the other side of the generator 2'7'from the high voltage terminal 28, is disposed on or immediately adjacent the insulating tube 21. In the embodiment of FIG. 3, the insulating tube 21 has an electrical conductor 32 applied to the exterior thereof. The conductor is electrically connected by a wire 32a to a tie rod 33 extending between the side frames of the press so as to ground the conductor 32 (FIG. 2). In the illustrated and preferred embodiment, the conductor is a diamond-shaped piece of metal and is applied to the central portion of the insulating tube 21. The conductor 32 may be of metallic sheet material which is cemented or otherwise fixed to the tube or may take various other forms as long as it provides the necessary conductive portion on the tube 21. The connection of the conductor 32 to ground establishes an electrostatic field between the conductor 32 and the bar 24 and this auxiliary field appears to radiate from the points at the longitudinal ends of the diamond and so alters the main field as to greatly increase the ionization between the cylinders 12 and the points of the needle 25 in the vicinity of the auxiliary field. Tests have shown that when the conductor 32 is on the bar 24, the field provided by the uniformly spaced needles will be nonuniform and will increase in magnitude as one proceeds from each end of the tube toward the longitudinal center of the tube.

In the preferred and illustrated embodiment, the conductor 32 is applied to the insulating tube 21 in a fixed position to control the electrostatic field established by the device 20. However, it may be desirable to be able to adjust the strength of various portions of the field by trial and error in order to secure the best results for a given stock or for given conditions of operation. Therefore, the present invention further contemplates the controlling of the field established by an electrostatic device by varying the position 'of one or more conductors applied to the insulating tube or material of the electrostatic device. Such an electrostatic device 40, which may be essentially of the same construction as the electrostatic device 29, is shown in FIG. 5. The electrostatic device 4ti, however, has a plurality of conductors corresponding to the conductor 32 and these conductors have been given the reference numeral 42. The conductors 42 are in the form of sheet metal clips of generally 0- cross section. The ends of the clips are adapted to be frictionally received and held Within parallel spaced grooves 44 which extend along the insulating tube of the device. The grooves 44 are on the side 'of the tube opposite the openings for the needles of the electrostatic device and the conductors 42 may be readily moved along the grooves to adjust their position along the length of the device. The conductors 42 have electrical connections fixed thereto for selectively grounding the portions to a wire 43 mounted on the insulating tube of the device 40. The connections for grounding the conductors are shown as wire connectors 45 connected between the conductors and the wire 43. To facilitate the attachment and detachment of the connectors to the wire 43, the connecting wires 45 are connected to the wire by a setscrew-type slidable connection on the wire 43.

The movable conductors 42 provide a convenient way for controlling the distribution of the field along the electrostatic device. By selectively grounding certain areas, the field strength pattern established by the device may be readily controlled and this control may be provided regardless of the spacing of the needles. The needles may be evenly spaced, or may have varying spacing. Moreover, the conductors 42 may take various forms which enable the portions of the insulating material to be grounded to be readily selected. The particular form of the conductive portion is not so important as the fact that the conductive portions may be selectively located at various areas to control the intensity of the field at the areas.

In the embodiment shown in FIG. 6, the grounded conductor is in the form of telescoping elements, which are connected to the insulating tube 'of a device 49 which basically corresponds in structure to the device 26 except for the conductor 32 which is replaced by the telescoping elements, at the central portion thereof on the side opposite to the ionizing needles. In this form, the electrostatic device has a plate 50 which is fixed to the insulating tube and tubular conducting means 51, 52 extend from the plate 50 toward respective ends of the insulating tube 53 of the device in close proximity thereto. The tubular conducting means 51, 52 are each comprised of a three-section telescoping conductor similar to conventional television antennas and these conductors include a tubular base conductor 51a, and intermediate section 52a, which telescopes into the base conductor 51a, and an outer tubular section 51c which telescopes into the intermediate section 51b. By telescoping the sections 51a-51b and extending the sections, the field strength established by the electrostatic device is rendered nonuniform in a controllable manner. The extension of the conductor 51 will establish a field between the extended conductor 51 and the internal conductive bar 54- of the device and increase the field strength in the area to which it is extended. Similarly, the conducting means 52 is made up of telescoping sections and the pattern of field strength on the side of the base plate 50 toward which the conducting means 52 extends can be controlled by extending and telescoping the conductor 51a.

In the illustrated embodiments, the field is controlled by placing a conductor immediately adjacent selected areas of the insulating tube 21 and connecting that conduct'or to the opposite side of the power supply to which the needles are connected. This establishes a field between the conductor and the bar 24. In the aforesaid Brandt application, the strength of the field is controlled by varying the spacing of the needles 25 to provide a nonuniform field. If, however, the insulating tube is used as in the disclosed embodiment to protect operating personnel from accidental shock, the spacing of the needles loses its effect to control the field pattern and the device tends to produce a substantially uniform field. Tests have shown, however, that a conductor such as the conductor 32 may be applied to the tube and positioned so that the electrostatic field established by the device has a pattern which is in accordance with the spacing of the needles.

It can now be seen that the present invention has provided a new and an improved electrostatic device for establishing a varying field in which the electrostatic device does not constitute a hazard to operating personnel in the area and which is constructed and arranged so that the field established by the device may have varying intensities in different portions thereof and so that the distribution of the various intensities can be readily varied.

While preferred embodiments of the present invention have been described in considerable detail, it is hereby our intention to cover all such modifications, constructions, and arrangements which fall within the ability of those skilled in the art and within the scope and spirit of the present invention.

Having described our invention, we claim:

1. An electrostatic device comprising an elongated member for establishing an electrostatic field between the elongated member and a second member, aninsulating covering for said elongated member extending about said elongated member and having means open on one side for exposing the elongated member to establish the 6 field, a conductor on said insulating member intermediate the ends thereof and insulated from said elongated member, and connections for connecting the elongated member to one side of a high voltage supply and for connecting said conductor to the other side of said high voltage supply.

2. In combination, a first conductive member for establishing an electrostatic field between the first conductive member and a second conductive member spaced from said first conductive member, a high voltage power supply having opposite sides connected to said conductive members to establish an electrostatic field therebetween, an insulating material covering said first conductive member and having opening means therein on the side thereof facing said second conductive member to expose said first conductive member, and means for establishing nonuniformity in the electrostatic field between said members comprising a third conductive member disposed adjacent a portion of said insulating material removed from said opening means and connected to the side of said power supply to which said second conductive member is con- ,nected.

3. In combination, a first conductive member for establishing an electrostatic field between the first conductive member and a second conductive member spaced from said first conductive member, a high voltage power supply having opposite sides connected to said conductive members to establish an electrostatic field therebetween, an insulating material covering said first conductive member and having opening means therein on the side thereof facing said second conductive member to expose said first conductive member, and means for establishing nonuniformity in the electrostatic field between said members comprising a third conductive member disposed adjacent a portion of said insulating material removed from said opening means and connected to the side of said power supply to which said second conductive member is connected, said first conductive member including a plurality of needles extending from said first conductive member toward said second conductive member adjacent said opening means and said third conductive means being disposed on the side of said insulating material remote from said opening means.

4. An electrostatic device for establishing an electrostatic field between a first conductive member and a sec ond conductive member, an insulating covering for said first conductive member extending about said member and open on the side thereof facing said second conductive member for exposing the first conductive member to establish the field, a conductor on said insulating member intermediate the ends thereof and insulated from said first conductive member and means for connecting the first conductive member to one side of an electrostatic power supply and for connecting said conductor to the other side of said supply, said first conductive member having a plurality of needles extending from said first conductive member toward said second conductive member.

5. An electrostatic device comprising an elongated member for establishing an electrostatic field between the elongated member and a second member, an insulating covering for said elongated member extending about said elongated member and having means open on one side for exposing the elongated member to establish the field, a conductor on said insulating covering intermediate the ends thereof and insulated from said elongated member, connections for connecting the elongated member to one side of a high voltage device and for connecting said conductor to the other side of the high voltage device, and means supporting said conductor for adjustment along the side of the insulating covering remote from said opening means.

6. An electrostatic device as defined in claim 5 including a plurality of adjustable conductors on said electrostatic device.

7. In combination, a first conductive member for establishing an electrostatic field between the first conductive member and a second conductive member spaced from said first conductive member, a high voltage power supply having opposite sides connected to said conductive members to establish an electrostatic field therebetween, an insulating material covering said first conductive member and having opening means therein on the side thereof facing said second conductive member to expose said first conductive member, and means for establishing nonuni formity in the electrostatic field between said members comprising a third conductive member disposed adjacent a portion of said insulating material removed from said opening means and connected to the side of said power supply to which said second conductive member is connected, said third conductive member being adjustable along the side of the insulating material remote from said opening means and said first conductive member having a plurality of needles extending therefrom toward said second conductive member.

8. In combination, a first conductive member for estab lishing an electrostatic field between the first conductive member and a second conductive member spaced from said first conductive member, a high voltage power supply having opposite sides connected to said conductive members to establish an electrostatic field therebetween, an insulating material covering said first conductive mem-- her and having opening means therein on the side thereof facing said second conductive member to expose said first conductive member, and means for establishing nonuni-- formity in the electrostatic field between said members: comprising a third conductive member disposed adjacent a portion of said insulating material removed from said opening means and connected to the side of said power supply to which said second conductive member is connected, said third conductive member comprising a telescoping conductor removed from said opening means and extensible and contractible along the length of said insulating material.

9. An electrostatic device comprising a tube of insulating material, a rodlike conductive member disposed within said tube and of smaller cross-sectional area than that of the inside diameter of the tube, a piurality of spaced parallel needles extending outwardly from one side of said rod, said tube having opening means in the side wall thereof adjacent the ends of said needles to expose the latter, and a second conductive member on said tube intermediate the ends thereof, said second conductive member being on the side of said tube remote from said opening means.

10. An electrostatic device comprising a tube of insulating material, a rodlike conductive member disposed within said tube and of smaller cross-sectional area than that of the inside diameter of the tube, a plurality of spaced parallel needles extending outwardly from one side of said rod and terminating short of the outer periphery of the tube, said tube having opening means in the side wall thereof adjacent the ends of said needles to expose the latter, and a second conductive member on said tube intermediate the ends thereof, said second conductive member being on the side of said tube remote from said opening means and said second conductive member being adjustable along the length of the tube.

11. A machine for performing an operation on sheet material, a movable member with which said sheet material is to move in one direction and electrostatic means for causing said sheet material to hug said member comprising an elongated conductive member spaced from said movable member for establishing an electrostatic force field at different magnitudes between said members proceeding across said material transversely to the direction of movement, means for connecting said movable member and said conductive member to first and second sides of a power supply for establishing said electrostatic field, and means for varying the relative magnitudes of portions of said field comprising a conductor disposed adjacent said conductive member on the side thereof remote from said movable member, and means for connecting said conductor to said first side of said power supply.

12. The combination as defined in claim 11 wherein said conductive member is covered with an insulating material having opening means on the side of said conductive member facing said movable member to expose the conductive member and wherein said conductor is disposed immediately adjacent the exterior of said insulating material.

13. An electrostatic device comprising a tube of insulating material, an elongated conductive member disposed Within said tube andhaving a smaller cross sectional area than the inside of the tube to provide an air space between the tube and elongated member which extends along the length of the latter, a plurality of spaced parallel needles extending outwardly from one side of said conductive member, said tube having an opening means in the wall thereof adjacent the ends of said needles to expose the latter and said tube including electrically conductive means intermediate the ends thereof and electrically insulated from said conductive memher to control the effect of said tube on said field.

14. An electrostatic device comprising a tube of insulating material, an elongated conductive ionizing member disposed within said tube and having a smaller cross sectional area than the inside of the tube to provide .an air space between the tube and ionizing member extending along the length of the latter, said tube having an opening means in the wall thereof to expose one side of said ionizing member and said tube including electrically conductive means intermediate the ends thereof and electrically insulated from said conductive member to control the effect of said tube on said field.

15. An electrostatic device comprising a rod-like conductive member having a plurality of ionizing needles extending outwardly from one side thereof, an insulating member for said conductive member disposed adjacent said conductive member and extending therealong, and movable conductive means on said insulating memher for adjusting the strength of the electrostatic field adjacent said conductive means.

16. An electrostatic device comprising an elongated insulating member, an elongated conductive member supported in said insulating member so as to be covered thereby, said elongated conductive member having a plurality of ionizing projections extending outwardly therefrom to one side thereof, said insulating member having wall means extending to said one side of said conductor and beyond said projections on the opposite sides thereof with said wall means defining opening means outwardly of said projections on said one side of said conductive member for exposing said projections, and conductive means supported by said insulating member and insulated from said conductive member for controlling the eifect of said insulating member on the field established by said conductive member.

17. In combination, a first elongated conductive-member for establishing an electrostatic field between the first conductive member and a second conductive member spaced from said first conductive member, a high voltage power supply having opposite sides connected to said conductive members to establish an electrostatic field therebetween, said elongated conductive member having a plurality of ionizing projections extending to one side thereof toward said second conductive member, an insulating envelope covering said first conductive member and having wall means on opposite sides of said projections extending beyond said projections toward said second conductive member, said wall defining opening means on the side of said elongated conductive said insulating envelope and insulated from said elongated conductive member, and means connecting said conductive means to the side of said power supply to which said second conductive member is connected.

18. An electrostatic device comprising an elongated insulating member, an elongated conductive member supported in said insulating member so as to be covered thereby, said elongated conductive member being adapted to establish an ionizing field, said insulating member having wall means defining opening means for exposing said conductive member, and conductive mean supported by said insulating member and insulated from said conductive member for controlling the efiect of References Cited by the Examiner UNiTED STATES PATENTS 1,169,428 1/10 Rogers.

2,152,077 3/39 Meston.

2,667,121 1/54 Huebner.

2,980,834 4/61 Tregay 317-262 3,039,388 6/62 Brandt 101-232 3,082,735 3/63 Vaccaro 226-195 X ROBERT B. REEVES, Acting Primary Examiner. 

1. AN ELECTROSTATIC DEVICE COMPRISING AN ELONGATED MEMBER FOR ESTABLISHING AN ELECTROSTATIC FIELD BETWEEN THE ELONGATED MEMBER AND A SECOND MEMBER, AN INSULATING COVERING FOR SAID ELONGATED MEMBER EXTENDING ABOUT SAID ELONGATED MEMBER AND HAVING MEANS OPEN ON ONE SIDE FOR EXPOSING THE ELONGATED MEMBER TO ESTABLISH THE FIELD, A CONDUCTOR ON SAID INSULATING MEMBER INTERMEDIATE THE ENDS THEREOF AND INSULATED FROM SAID ELONGATED MEMBER, AND CONNECTIONS FOR CONNECTING THE ELONGATED MEMBER TO ONE SIDE OF A HIGH VOLTAGE SUPPLY AND FOR CONNECTING SAID CONDUCTOR TO THE OTHER SIDE OF SAID HIGH VOLTAGE SUPPLY. 